Magnetic resonance acquisition to determine the lumen length of a tortuous phantom aorta.

PURPOSE: Endovascular abdominal aortic aneurysm repair is a technique that requires an accurate measurement of the aneurysm's lumen length prior to the procedure. This study examines the accuracy of luminal length measurement in an aortic phantom using magnetic resonance angiography (MRA) axial source images. METHODS AND RESULTS: Tortuous phantom aortas were constructed using water-filled plastic tubing (7 mm in diameter with lengths of 80 to 160 mm). The tubes were molded into three-dimensional "S" or "C" shapes that simulated the luminal course of a tortuous aorta. Phantoms were imaged at angles of 0 degrees, 15 degrees, 30 degrees, and 45 degrees to the image slice direction on a 1.5T Signa MR scanner using a transaxial two-dimensional time-of-flight (TOF) and a T1-weighted spin-echo acquisition. The luminal length of the phantom was calculated after establishing the lumen center coordinates in axial source images and then measuring the distance between two sequential slices using the Pythagorean theorem. The accuracy of this measurement in the phantom was 89% to 99.6%, proportional to the length of the tubing. Accuracy was not affected by angulation of < 45 degrees. CONCLUSION: Two-dimensional TOF MRA source images can provide an accurate measurement of the phantom aorta's lumen length.

Cost-effectiveness of echocardiography: a private practice perspective.

Echocardiography is essential to the modern practice of cardiology. It is a robust, noninvasive technique, with proven effectiveness in the diagnosis of a multitude of cardiac disorders. However, the true costs of echocardiography and the charges, reimbursement, and collection rates, plus the overall economic value of echocardiography relative to other technical and cognitive services provided by cardiologists, are not so clearly understood or established. The purpose of this article is to provoke thought among echocardiographers about these economical issues.

Can pleural effusions cause tamponade-like effects?

Experimental studies have confirmed the clinical impression that large bilateral pleural effusions are able to raise the pressure in an otherwise hemodynamically insignificant pericardial effusion to a level sufficient to produce right ventricular diastolic collapse (RVDC). The hemodynamic consequences of this syndrome are not as severe as when the intrapericardial pressure is raised to the same level by excess intrapericardial fluid in the absence of pleural effusions. RVDC caused by excess pleural fluid with a minor pericardial effusion is a false positive indication for pericardial fluid drainage. Thoracentesis is more appropriate.

Pleural effusion as a cause of right ventricular diastolic collapse.

BACKGROUND: We hypothesized, after seeing several suggestive clinical examples, that a process leading to a large bilateral pleural effusion in the presence of an otherwise insignificant pericardial effusion could result in right ventricular diastolic collapse (RVDC) as seen by two-dimensional echocardiography. This noninvasive marker for hemodynamically significant cardiac tamponade occurs when pericardial fluid is under pressure. Therefore, RVDC resulting from a large pleural effusion would represent a false-positive indication of cardiac tamponade caused by excessive pericardial fluid. METHODS AND RESULTS: Seven spontaneously breathing dogs were chronically instrumented to measure ascending aortic, right atrial, intrapericardial, intrapleural, left atrial, and pulmonary artery pressures and cardiac output. Intravascular volume was adjusted before each experiment to the euvolemic range with saline solution. The onset of RVDC was observed in each animal by two-dimensional echocardiography during seven paired episodes of tamponade induced by infusions of warm saline into the pericardial space alone and, after drainage of the pericardial fluid and complete recovery, into the pleural space in the presence of a small pericardial effusion. The onset of RVDC occurred at the same intrapericardial (8.17 versus 9.47 mm Hg) and right atrial (7.41 versus 7.46 mm Hg) blood pressures regardless of whether it was produced by an intrapericardial or an intrapleural effusion but began in expiration during the former and in inspiration during the latter. Intrapericardial pressure increased in the same manner as intrapleural pressure during intrapleural saline infusion. Nevertheless, cardiac output and aortic blood pressure were better preserved, and at the onset of RVDC, the pulmonary artery systolic blood pressure was higher (p less than 0.0001) and the degree of pulsus paradoxus lower (p less than 0.01) with intrapleural infusion. CONCLUSIONS: These results indicate that a large bilateral pleural effusion can elevate intrapericardial pressure sufficiently to cause RVDC and, perhaps, lead to misdirected therapy of an otherwise insignificant pericardial effusion.

Evaluation of leg perfusion during exercise using technetium 99m sestamibi. A new test for peripheral vascular disease.

Thirty patients with occlusive peripheral vascular disease underwent clinical examination, segmental blood pressure determinations, intra-arterial digital subtraction angiography, and treadmill stress testing with injection of technetium 99m sestamibi at peak exercise. Radionuclide images of the thighs, calves, and feet showed clear delineation of major muscle groups. Diminished radiotracer distribution was closely correlated with the presence of occlusive vascular disease on angiography and with the presence of claudication and reduced segmental blood pressure. A quantitative scheme based on pixel intensity was developed to compare areas of regional perfusion.

Diagnostic reliability of radionuclide ventriculography in detecting left ventricular hypertrophy. Echocardiographic and ECG correlations.

Left ventricular hypertrophy (LVH) is frequently present in patients referred for radionuclide ventriculography (RVG) for evaluation of left ventricular function. During interpretation of these studies, the nuclear medicine physician may have the subjective impression that increased septal thickening is present because of the abnormally prominent separation of the right and left ventricular blood pools. To examine the diagnostic reliability of this finding, we retrospectively reviewed the RVG studies of 43 consecutive patients and correlated the finding of subjectively increased septal thickness with established echocardiographic (ECHO) criteria and commonly used electrocardiographic (ECG) indices of LVH. Using standard ECHO measurements of septal thickness as a gold standard, RVG interpretation of septal thickening demonstrated a sensitivity of 0.69, specificity of 0.70, and accuracy of 0.70. When compared with standard ECG criteria for LVH, RVG performed quite favorably in the diagnosis of LVH confirmed by ECHO left ventricular mass index. We conclude that scintigraphic evidence of LVH should be reported when RVG studies are interpreted.

Static versus dynamic exercise: effects on Doppler echocardiographic indices of left ventricular performance.

In order to compare the effects of static exercise with those of dynamic exercise on the Doppler echocardiographic measurements of ascending aortic blood flow velocity and acceleration, Doppler echocardiography was performed with sustained handgrip exercise and with supine bicycle exercise in 12 normal subjects, 12 patients with coronary artery disease, and 7 patients with heart failure. In normal subjects: peak velocity decreased by 16 +/- 11% with handgrip from the resting value and increased by 49 +/- 19% with bicycle exercise (p less than 0.01); mean acceleration decreased by 6 +/- 30% with handgrip and increased by 162 +/- 83% with bicycle exercise (p less than 0.01). In patients with coronary artery disease: peak velocity declined by 9 +/- 14% with handgrip and increased by 19 +/- 18% with bicycle exercise (p less than 0.01); mean acceleration increased by 13 +/- 27% with handgrip and by 41 +/- 33% with bicycle exercise (NS). In patients with congestive heart failure: peak velocity decreased by 19 +/- 13% with handgrip and increased by 5 +/- 17% with bicycle exercise (p less than 0.01); mean acceleration decreased by 12 +/- 23% with handgrip and by 4 +/- 37% with bicycle exercise. A marked increase in afterload stress induced by static exercise presumably offsets the moderately increased contractility and accounts for the decline of peak velocity and mean acceleration with static exercise both in normals and cardiac patients. In contrast, marked increase in contractile state along with little change in afterload with dynamic exercise results in markedly increased peak velocity and mean acceleration in normal subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of ultrasonic tissue characterization to distinguish reversible from irreversible myocardial injury.

Tissue characterization reflects structural and functional integrity of tissues. Inasmuch as reversible ischemia causes no structural damage and irreversible ischemia results in persistent structural myocardial damage, we postulated that ultrasonic tissue characterization can distinguish the two types of injuries. Anesthetized open chest dogs underwent 15 minutes (group 1, n = 5) and 90 minutes (group 2, n = 8) of acute total occlusion of the left anterior descending coronary artery, followed by 3 hours of reperfusion. Myocardial ischemia-infarction was confirmed with segment shortening, electronmicroscopic examination, and triphenyl tetrazolium chloride staining. Integrated backscatter Rayleigh 5 (IBR5), a measure of ultrasonic backscatter, and Fourier coefficient of amplitude modulation (FAM), an index of cardiac cycle dependent variation in backscatter, were measured at baseline, during ischemia, and after reperfusion. Group 1 (reversible ischemia) showed an increase in IBR5 from -48 +/- 1.2 dB at control to -45 +/- 1.0 dB (p less than 0.01) during ischemia, which returned to baseline after reperfusion (-47 +/- 1.3 dB). FAM was blunted during ischemia (6.2 +/- 1.0 dB during control versus 1.2 +/- 1.0 dB during ischemia, p less than 0.01) and recovered completely during reperfusion. Segment shortening was abolished during ischemia (18% +/- 3% during control versus -12% +/- 5% during ischemia, p less than 0.01) and recovered partially during reperfusion (4% +/- 5%). The group 2 animals with irreversible myocardial injury showed an increase in IBR5, from -49 +/- 1.2 dB during control to -44 +/- 1.0 dB during ischemia (p less than 0.01) and paradoxical bulging of the ischemic region (17% +/- 3% to -7% +/- 3%, p less than 0.01) during ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular regulation during head-out water immersion exercise.

Head-out water immersion is known to increase cardiac filling pressure and volume in humans at rest. The purpose of the present study was to assess whether these alterations persist during dynamic exercise. Ten men performed upright cycling exercise on land and in water to the suprasternal notch at work loads corresponding to 40, 60, 80, and 100% maximal O2 consumption (VO2max). A Swan-Ganz catheter was used to measure right atrial pressure (PAP), pulmonary arterial pressure (PAP), and cardiac index (CI). Left ventricular end-diastolic (LVED) and end-systolic (LVES) volume indexes were assessed with echocardiography. VO2max did not differ between land and water. RAP, PAP, CI, stroke index, and LVED and LVES volume indexes were significantly greater (P less than 0.05) during exercise in water than on land. Stroke index did not change significantly from rest to exercise in water but increased (P less than 0.05) on land. Arterial systolic blood pressure did not differ between land and water at rest or during exercise. Heart rates were significantly lower (P less than 0.05) in water only during the two highest work intensities. The results indicate that indexes of cardiac preload are greater during exercise in water than on land.

Quantitative ultrasonic assessment of normal and ischaemic myocardium with an acoustic microscope: relationship to integrated backscatter.

PURPOSE OF INVESTIGATION: The aim was to study ultrasonic propagation properties of normal and ischaemic myocardium with a scanning laser acoustic microscope and to correlate these changes with ultrasonic backscatter. DESIGN: Myocardial ischaemia was produced by total occlusion of left anterior descending coronary artery in anaesthetised open chest dogs. Myocardium supplied by left circumflex coronary artery served as normal control. IBR5, an optimum weighted frequency average (4-6.8 MHz) of the squared envelope of diffraction corrected backscatter, was measured in vivo. Ultrasonic attenuation coefficient, an index of loss per unit distance, the propagation speed and heterogeneity index were measured from normal and ischaemic regions with a scanning laser acoustic microscope which operates at 100MHz in vitro. Myocardial water content of normal and ischaemic myocardium was also estimated. SUBJECTS: Were five anaesthetised mongrel dogs. RESULTS: Attenuation coefficient of 33.8(SD4.2) dB.mm-1 in the ischaemic tissue was lower than 63.8(17.2) dB.mm-1 in the normal tissue (p less than 0.01). Ultrasonic speed was lower in ischaemic than normal myocardium at 1584(25) v 1612(35) m.s-1 (p less than 0.05). Heterogeneity index of 11(7) m.s-1 in the ischaemic region was lower than 14(8) m.s-1 in the normal region (27% reduction, p less than 0.05). IBR5 and myocardial water content were higher in the ischaemic than the normal myocardium: -37.2(SEM1.8) dB v -46.6(0.6) dB, (p less than 0.01) and 80.9(0.0)% v 78(0.2)%, (p less than 0.05) respectively. CONCLUSION: Ultrasonic properties of the myocardium are significantly altered during acute ischaemia.

Ultrasonic tissue characterization of normal and ischemic myocardium.

Cardiac ultrasonic tissue characterization is designed to use the alterations in acoustic signals from the myocardium to differentiate normal from ischemic or infarcted tissue due to their characteristic backscatter attenuation. Various approaches such as use of a gray scale, color display, or quantitative image analysis have been used for tissue characterization, but all depend on subjective assessments and are not necessarily reproducible. The most promising method has been the use of "raw" radiofrequency signals and measure changes in the ultrasonic attenuation with an index of backscatter to distinguish normal from abnormal myocardium called "integrated backscatter" (IB). Various studies have demonstrated the changes in the ultrasonic backscatter with ischemia or infarction. In this review we summarize our experience with a research prototype instrument in tissue characterization and differentiation of normal, ischemic, infarcted, and post ischemic reperfused myocardium in anesthetized open chest dogs. Currently we are investigating the role of ultrasonic tissue characterization to estimate infarct size and plan to apply these observations to patients in order to detect viable myocardium and quantitate infarct size.

Doppler echocardiographic evaluation of left ventricular function.

Invasive measurements of maximum acceleration of aortic blood flow are sensitive indicators of left ventricular function. Doppler echocardiography provides noninvasive measurements of aortic blood flow acceleration. Our studies establish the accuracy of Doppler-derived indices of aortic blood flow velocity for evaluation of left ventricular function. Doppler-derived peak velocity and mean acceleration showed excellent correlation with invasively measured peak left ventricular dP/dt and maximum aortic blood flow (dQ/dt) under varying heart rate, preload, afterload, and inotropic states. Similar correlations were observed between Doppler-derived peak velocity and mean acceleration and invasively measured left ventricular dP/dt and dQ/dt under conditions of varying degrees of myocardial ischemia. Thus, Doppler echocardiography provides an accurate noninvasive method to evaluate left ventricular performance.

The effect of regional myocardial ischemia on Doppler echocardiographic indexes of left ventricular performance: influence of heart rate, aortic blood pressure, and the size of the ischemic zone.

Doppler echocardiographic indexes of ascending aortic blood flow velocity have been found to be an effective method of assessing changes in left ventricular performance induced by myocardial ischemia in both experimental animal preparations and in patients. In eight opened-chest anesthetized dogs, we investigated the influence of heart rate, aortic blood pressure, and size of the ischemic zone on Doppler indexes during regional myocardial ischemia. With control of mean aortic blood pressure and heart rate, transient coronary artery occlusion resulted in a statistically significant decline in peak velocity and mean velocity when as little as 24% of left ventricular myocardium was rendered ischemic. However, when heart rate and mean aortic blood pressure were not controlled, significant declines in peak velocity and mean velocity occurred only with simultaneous two-vessel occlusions involving greater than 47% of left ventricular myocardium. Although transient coronary artery occlusions generally produced no significant change in heart rate in the absence of atrial pacing, significant declines in aortic blood pressure were observed. We conclude that Doppler indexes of left ventricular performance obtained during myocardial ischemia are influenced not only by the extent of myocardium rendered ischemic, but also by changes in mean aortic blood pressure.